[Scala] add async support to Scala API client

[wing328]

PR checklist

• Read the contribution guidelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates)
• Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

Based on #4855

cc @clasnake

[wing328]

@clasnake there's a PR by @ePaul to add back the missing dependencies for joda time: #5092

If I remember correctly, we encountered issue with java.util.Date in the Java API client and therefore @cbornet introduced other datetime libraries (e.g. joda) to address the issue.

[wing328]

@clasnake CI (travis) reported errors. Here is part of the error messages:

[ERROR] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala/io/swagger/client/AsyncClient.scala:5: error: object wordnik is not a member of package com
[ERROR] import com.wordnik.swagger.client._
[ERROR]            ^
[ERROR] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala/io/swagger/client/AsyncClient.scala:9: error: not found: type SwaggerConfig
[ERROR] class AsyncClient(config: SwaggerConfig) extends Closeable {
[ERROR]                           ^
[ERROR] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala/io/swagger/client/AsyncClient.scala:15: error: not found: type TransportClient
[ERROR]   protected def transportClient: TransportClient = new RestClient(config)
[ERROR]                                  ^
[ERROR] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala/io/swagger/client/AsyncClient.scala:15: error: not found: type RestClient
[ERROR]   protected def transportClient: TransportClient = new RestClient(config)
[ERROR]                                                        ^
[ERROR] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala/io/swagger/client/api/PetApi.scala:32: error: object wordnik is not a member of package com
[ERROR] import com.wordnik.swagger.client._
[ERROR]            ^

Ref: https://s3.amazonaws.com/archive.travis-ci.org/jobs/212403027/log.txt

I wonder if you can take a look as I might have made mistakes when resolving conflicts during the cherry-pick.

[clasnake]

@wing328 No problem. I'll take a look. Do I have the permission to update this pr directly? Or shall I create a new one against this one or do you have any other suggestions?

[wing328]

@clasnake I don't think you've permission as the PR is in the official repo.

Please feel free to submit against this one (pr4855_cherrypick) or 2.3.0.

[wing328]

Closed via #5115